Linear regulators are a class of voltage regulators where output voltage is controlled by varying voltage drop across a series-pass element, typically a transistor. Linear regulators have significant advantages over other types of voltage regulators in certain applications. For example, linear regulators do not generate switching noise, and linear regulators do not incur switching losses. Additionally, linear regulators do not require energy storage inductors, thereby promoting small regulator size, low regulator cost, and fast transient response. Furthermore, linear regulators can achieve high efficiency in low-current applications and/or in applications where output voltage magnitude is close to input voltage magnitude.
FIG. 1 illustrates a conventional linear regulator 100 including a transistor 102, an output capacitor 104, and control circuitry 106. Transistor 102 is electrically coupled between an input node 108 and an output node 110 to form a series-pass element. Output capacitor 104 is electrically coupled between output node 110 and a reference node 112 to help maintain regulation of an output voltage Vo during transient load events. Control circuitry 106 is configured to control transistor 102 to maintain a desired output voltage Vo. In particular, control circuitry 106 monitors output voltage Vo, and control circuitry 106 drives transistor 102 such that transistor 102 has as requisite voltage drop Vt to achieve the desired output voltage Vo. Consequently, control circuitry 106 will vary an operating point of transistor 102 according to operating conditions of linear regulator 100, to maintain regulation of output voltage Vo. For example, if magnitude of an input voltage Vi increases, control circuitry 106 will vary the operating point of transistor 102 to increase voltage drop Vt, to maintain desired output voltage Vo.